This invention relates to improved control circuit arrangements for electrical appliances and more particularly to a circuit arrangement for controlling the operating temperature of an appliance.
In one form of electrical appliance, an electrical resistance heater element is mounted within a casing and an airstream is established which flows through the casing and about the heater element. The airstream which is thus heated is discharged from an outlet aperture of the casing and is utilized for hair treatment by curling, styling, or drying.
An appliance of this type can, at times, experience a malfunction which is caused by a defective component of the appliance. Since this malfunction is generally characterized by an overheating of the appliance, a control circuit is provided for sensing the occurrence of this condition and for automatically de-energizing the appliance. The control circuit includes a thermostat which is positioned in the heated airstream and operates to interrupt the application of an energizing potential to the heater element. This operation of the thermostat disables use of the appliance and the user properly seeks service to correct the malfunction.
It has been found however that the overheating which is generally characteristic of a malfunction can also occur in the absence of a malfunction. This has been found to be the case, for example, when the airstream is temporarily restricted by means external to the appliance. A substantially reduced airflow without concurrent reduction in electrical energization of the heater results in overheated operation of the appliance. This condition occurs frequently in hair treatment devices when hair strands gather at an airstream inlet or outlet to the casing and create a restriction to airflow. The airstream which thus overheats causes the thermostat to interrupt energization of the heater. While the simple removal of the inlet blockage will correct overheating and reestablish normal operating conditions, the appliance user at times is confused with the reaction of the appliance under these conditions. Consequently, the user generally initiates unnecessary and costly service examinations of the appliance which are an inconvenience to the user and an expense to the manufacturer.
Accordingly, it is an object of this invention to provide an improved control circuit arrangement for an electrical appliance.
Another object is to provide an improved control circuit arrangement for automatically reducing energization of a heater upon overheating of the appliance;
Another object is to provide an improved control circuit arrangement which automatically reduces the energization of the heater upon airstream blockage.